It is convenient for a user to use a data card (hereafter, refer to a prepaid card) in which no change in payment is required in many application examples such as a public telephone, a parking meter, an automatic vending machine and traffic facilities. No cash is used in a device receiving the card so that damages such as destruction for the purpose of a theft, etc. are avoided. Therefore, there are advantages of lengthening a device life, etc.
Among such prepaid cards, a capacitive data card constituting one portion of a circuit having a capacitor comes to public notice as a data card with low price and low energy. A prepaid card system of this capacitive type is already registered as U.S. Pat. No. 4,280,119 on Jul. 21, 1981.
International Application WO95/14285 of May 26, 1995 discloses a prepaid card system with a fuse built in a circuit of the capacitive data card. When this fuse is intact, the fuse is in a state in which an electric current flows through this fuse. When the fuse blows out, resistance of the circuit is substantially increased. Therefore, a bit of data is represented by a resistance state of the fuse.
As shown in FIG. 14, this capacitive data card can form a circuit 3 having capacitors only when a card section 1 is integrated with a sensor section 2 formed on a reader side.
This card section 1 has a resistor R1 and electrode portions 1a, 1b each forming one portion of a capacitor connected to each terminal of this resistor R1. A sensor section 2 has electrode portions 2a, 2b each forming one portion of the capacitor connected to each terminal of a power source 4. When the card section 1 is set to the sensor section 2, a circuit having air capacitors 3a, 3b having air between the electrode portions is formed as shown in FIG. 14.
When the resister R1 in the circuit 3 formed as mentioned above is burned out by flowing an electric current having a high voltage through the resistor R1, the resistor R1 is used up and a state of the resistor R1 which is not burned out represents an unused bit so that one closed circuit provides a signal of one bit. Therefore, it is possible to form a data card in which a signal having a required digit number can be stored by forming an arbitrary number of closed circuits.
However, in the above conventional capacitive data card, bits are changed from an unused state to a used state by burning out the resistor R1 so that data cannot be easily regenerated. Accordingly, since data are not easily regenerated, alteration of the data is prevented and the capacitive data card has high reliability as merits. However, a constant limit is imposed on update of data stored in the card so that a problem exists in that utility value of the card cannot be sufficiently fulfilled.
In consideration of such a situation, the present invention provides a capacitive data card with high utility value and high reliability, and also provides a reader of this capacitive data card.